Conventionally, various reclining apparatuses for vehicle seats are suggested. Generally, reclining apparatuses for vehicle seats are utilized for reclining a seat back relative to a seat cushion. Such reclining apparatuses for vehicle seats include a lock mechanism provided each right and left side of a seat for restricting rotation of the seat back relative to the seat cushion. Switching operations (lock, unlock) of the lock mechanism enables to adjust the seat back to a desired reclining angle preferable for an occupant to have a seat and to retain the desired reclining angle.
For example, a reclining apparatus for a vehicle disclosed in JP2001-299489A (Patent document 1) includes a spring (18) wound around a rotational shaft of a connecting shaft (17) for connecting lock mechanisms provided at right and left sides of a seat. A first end of the spring is connected to a lower plate (7). A second end of the spring is connected to the connecting shaft. The spring biases a cam (16) of each lock mechanism through the connecting shaft so that a teeth portion (13) of an upper plate (8) engages with a teeth portion (12) of a pawl (11) of each lock mechanism to restrict rotation of a seat back relative to a seat cushion. However, because the spring biases each cam through the connecting shaft, if there is an assembly error between the right and left lock mechanisms in a rotational direction caused by, for example, strain of a seat frame or a floor surface, there is a possibility that, while one of the lock mechanisms can retain engagement described above, the other of the lock mechanisms cannot retain the engagement caused by insufficient biasing force.
On the other hand, a reclining apparatus for a vehicle disclosed in JP2000-342368A (Patent document 2) includes a spring (5) wound around a rotational shaft of a cam (32). A first end of the spring is connected to a lower plate (1). A second end of the spring is connected to a groove portion (32f) of the cam. The spring biases the cam so that a teeth portion (25a) of an upper plate (2) engages with a teeth portion (33a) of a pawl (33). Accordingly, rotation of a seat back relative to a seat cushion can be restricted without depending on a connecting shaft (4). An operational lever (7) is provided at the connecting shaft as a unit.
In the reclining apparatus for the vehicle disclosed in the Patent document 2, there is a fit clearance between the connecting shaft and the cam. The width of the fit clearance is set to a value sufficient for absorbing assembly error in a rotational direction between the right and left lock mechanisms. The fit clearance causes to generate a play of the operational lever in an operational direction corresponding to the rotational direction described above. Accordingly, operation of the operational lever is accompanied by uncomfortable feeling that the operational lever is not well restrained. There is also a possibility that the operational lever shakes in a range of the fit clearance and clatters with the connecting shaft, which results in noises, for example, at the time when a vehicle is in motion.
A need thus exists for a reclining apparatus for a vehicle seat, which can give comfortable operational feeling while an increase in number of parts is restricted. The present invention has been made in view of the above circumstances and provides such a reclining apparatus for a vehicle seat.